The present invention relates generally to quasi-optical systems. In particular, the present invention pertains to a quasi-optical system comprising quasi-optical grids (i.e., arrays or layers) with reconfigurable quasi-optical unit cells.
To accommodate bandwidth and resolution demands, future communication networks are likely to migrate toward operating frequencies at corresponding millimeter and sub-millimeter wavelengths. In the past, the lack of high-frequency semiconductor devices has prevented the development of such high-frequency systems. However, recent advances in semiconductor device technology have allowed integrated circuits to operate at as high as 300 GHz for transistors and 1.0 THz for diodes. In any working system, transmitters must be capable of efficiently providing sufficient power and the receivers must be able to handle signals of widely varying strength without sacrificing sensitivity. It seems exceedingly difficult to meet these demands using conventional microwave power-combining techniques.
One promising approach for realizing millimeter and sub-millimeter wavelength high power systems is quasi-optical power combining This is an elegant technique to integrate many active devices into a free-space power combining component. Hundreds, possibly thousands, of solid-state high speed devices could be incorporated through wafer scale integration to generate high power. Quasi-optical wireless systems are particularly attractive because they allow the front-end components to be inexpensively mass produced and they don""t require single mode waveguides, thereby allowing higher operating frequencies.
One of the key components in a complete quasi-optical system is the beam controller. The beam controller is used to control a beam by steering, focusing, splitting, switching, and/or shaping the beam. For example, the beam controller is used in systems employing radar for aircraft guidance, missile seeking, and automobile collision avoidance. Similarly, the beam controller is necessary in a millimeter wavelength imaging camera that sees through fog. In these systems, high speed control of a beam is necessary so that more targets can be tracked or imaged simultaneously.
In the past, beam switching has been demonstrated with beam switches comprising grids with PIN diodes. However, the configuration of the grids prevents them from being used to steer, focus, and/or shape beams.
Furthermore, beam controllers comprising grids with Schottky diodes have also been developed in the past for reflective steering of beams. However, the series resistance of the Schottky diodes increases when the operating frequencies increase. This causes significant reflection losses and prevents these beam controllers from being used at shorter wavelengths for a low loss system.
Therefore, there is a need for a quasi-optical beam controller that can efficiently operate at millimeter and sub-millimeter wavelengths without significant losses. Such a beam controller would ideally provide transmission type steering, focusing, and/or shaping of beams.